如何解决错误QXcbConnection：使用PHP的phantomJs使用exec函数时

导游：/var/www/html/phantom/index.js

var page = require('webpage').create();
var fs = require('fs');

page.open('http://insttaorder.com/',function(status) {
    // Get all links to CSS and JS on the page
    var links = page.evaluate(function() {

        var urls = [];

        $("[rel=stylesheet]").each(function(i,css) {
            urls.push(css.href);
        });

        $("script").each(function(i,js) {
            if (js.src) {
                urls.push(js.src);
            }
        });

        return urls;
    });

    // Save all links to a file
    var url_file = "list.txt";
    fs.write(url_file,links.join("n"),'w');

    // Launch wget program to download all files from the list.txt to current
    // folder
    require("child_process").execFile("wget",[ "-i",url_file ],null,function(err,stdout,stderr) {

                console.log("execFileSTDOUT:",stdout);
                console.log("execFileSTDERR:",stderr);

                // After wget finished exit PhantomJS
                phantom.exit();

            });

});

导游：/var/www/html/phantom/index.php

exec('/usr/bin/phantomjs  index.js 2>&1',$output);
echo '<pre>';
print_r($output);
die;

也尝试过

exec('/usr/bin/phantomjs  /var/www/html/phantom/index.js 2>&1',$output);
    echo '<pre>';
    print_r($output);
    die;

运行后,我得到低于错误

Array
(
    [0] => QXcbConnection: Could not connect to display
    [1] => PhantomJS has crashed. Please read the bug reporting guide at
    [2] =>  and file a bug report.
    [3] => Aborted (core dumped)
)

但是,如果我从终端运行index.php文件,如下所示：

user2@user2-H81M-S:/var/www/html/phantom$php index.php

然后它工作正常.我不知道如何解决它.请帮忙.

我正在使用以下版本
系统版本：Ubuntu 16.04.2 LTS
PHP版本：5.6
幻影版：2.1.1